Please note, that this is a translation of the German version of this page, which aims at mapping climbing sites like climbing areas, sectors, crags/boulders/... and of course halls. It also contains a JOSM-preset.
There is also a proposal for climbing, which discusses more detailed mapping like tagging single routes, pitches etc.

Tagging

This scheme should be preferably applied to nodes for artificial climbing walls. It may be applied to ways in conjunction with cliffs natural=cliff or for climbing halls with building=yes. The scheme also applies to boulders attached to bedrock natural=rock and free standing boulders natural=stone.

Grading

Usually individual climbing routes are graded according to their difficulty or danger. As only a crag or region but no individual routes are tagged, we have to specify a difficulty range.
This scheme takes account of numerous grading systems by including the system's name within the key. The proposal for climbing routes includes common names or acronyms for other grading systems such as "yds_class" for the Yosemite Decimal System class and "hueco" for the V-scale used with bouldering in the United States.